1. Field of the Invention
The invention relates to a turbo-machine compressor, more particularly a linkage for controlling the angles of incidence of the stator vane of the compressor.
2. Description of the Prior Art
The adjustment of the orientation of stator vanes of one or more stages of the compressor of a turbo-machine at a given rating is generally effected through the intermediary of links which are secured at one end thereof to a vane pivot whilst a second end thereof is pivotally connected on a ring capable of turning under the action of a drive device controlled by the regulatory system of the engine.
Fracture of a link gives rise to oscillation of the vane in question and consequently an adverse effect upon the aerodynamic efficiency of the compressor. Furthermore, in current advanced engines, the orientation of the vanes is calculated so as to reduce by a maximum amount the length of the compressor and because of this one vane deprived of its orientation control is liable to contact the rotor, giving rise to serious damage, even before reaching its oscillating condition.
Attempts have therefore been made to devise a security device limiting the amplitude of the accidental change in orientation of the vane.
Thus French Patent No. 2 524 934 describes a security device for a vne controlled at the tip, an arm secured to the root pivot and capable of turning through a limited angular range in a recess provided in the inner supporting the bearings of the root pivots.
Such a device only enables the "wild" vane to lock itself in two end orientations, defined by the abutment of the arm against the walls of a recess, independent of the orientation of the other vanes, and requires a substantial modification to the inner ring and to the root pivots.
According to another prior proposal, described in French Patent Specification No. 1 325 261, the vanes have platforms both at the tip and the root. These platforms are approximately circular but have two diametrically opposed flats. The platforms are mounted in casings so that the flats of two adjacent vanes leave a space enabling pivoting of vanes between two angular end orientations. The device serves to prevent or at least to minimize gas losses between the platforms in the two angular end orientations and it is not effective insofar as losses can arise at intermediate angular positions.
Similar devices having the same function are described for example in French Patent Specification No. 1 548 701 and British Patent Specification No. 1 324 385.
Such devices are capable of limiting the rotation of a vane in the case of failure of its control mechanism. However, they are bulky and require a substantial modification to the stator so as to receive the platforms. Furthermore, given the small dimensions necessary for the flats, they are not capable of controlling effectively a vane in an angular end orientation in relation to another in case of failure of the control link, and because of thus they give rise to undesirable friction and jamming.